The current invention relates to fan casings for gas turbine engines for aircraft, particularly to penetration resistant fan casings for containing fragmented engine parts.
Jet aircraft are powered by propulsion system, which includes a gas turbine engine housed within an aerodynamically streamlined nacelle. The typical engine includes a fan section with a rotatable hub connected to an array of fan blades projecting radially from the hub, and a fan case encircling the blades. In operation, engine parts (particularly portions of the fan blade) may become separated from the hub, which may include all or a portion of the blade becoming separated from the remainder of the blade. Fan casings are designed to contain the fragmented pieces within the casing.
Particularly in large diameter engines, a metallic case thick enough to resist penetration is prohibitively heavy. As such, the engines are often equipped with a containment structure, which includes a fabric wrapped around engine parts. The fabric is often a light-weight, high strength ballistic fabric such as Kevlar® (a trademark of E.I. Dupont de Nemours & Company). The containment fabric is wrapped in multiple layers around a relatively thin, often penetrable supporting case. Thus, the portion of the blade becomes separated from the rest of the engine, the fragment penetrates the support case and strikes the fabric. The fabric deflects radially, and at least some of the fabric layers remain intact to capture and contain the fragment.
Containment systems which include fabric are more weight efficient than metallic containment cases, but nonetheless add considerable weight to the engine. The fabric must be designed to be light-weight, but to maintain its durability. If the fabric deflects excessively, the fragmented engine part can strike or damage the interior of the nacelle, resulting in a pierced fabric. Thus, it is desirable to have a fabric that is durable but within minimized weight that will not compromise containment capability or risk damage to the nacelle.